The aim of this proposal is to study some of the morphological and biochemical processes involved in the formation of tubular enamel in the American opossum, Didelphis marsupialis. The project has three main parts: (1) To study the normal events of amelogenesis by standard transmission electron microscopy. (2) To observe the enamel tubules (about 0.2 Mum in diameter, in this species) by high voltage electron microscopy. (3) To analyze the enamel proteins of the developing extracellular matrix. Results of this study will fill a gap in the literature, since few previous studies have addressed the question of developing enamel tubules with modern techniques. The present study will emphasize matrix-mineral interactions to determine which factors or structures might be responsible for the formation of an enamel which is not as fully mineralized as most other mammalian enamels. This approach could enlighten our knowledge of certain dental pathologies where disturbances in mineralization exist. Correlation of biochemical and structural data to functional demands on the teeth during mastication might increase our knowledge of the selective pressures for certain ameloblast cell products. Future studies will go into much more detail on the biochemistry of the matrix and attempt to label specific enamel components. The present investigation, however, will clarify the structural events and begin the study of the biochemical events involved in the formation of enamel tubules.